From Gene to Protein: Transcription & RNA Processing Chapter 17.1-17.3

Important Terms to Know… 25% of students confuse these terms in FRQs!! Replication Copying of DNA prior to cell division (DNA  DNA) Not prior to transcription! Transcription Making mRNA copy from DNA prior to protein synthesis (DNA  RNA) Translation Decoding mRNA and making a protein (RNA  Protein)

17.1 Genes specify proteins via transcription and translation

Understanding Genes  Proteins Scientists connected metabolic disorders to genes Ex: alkaptonuria Urine blackens when exposed to air due to missing enzyme that metabolizes alkapton Beadle & Tatum studied bread mold Introduced mutations and saw that mutating certain genes caused metabolic defects One gene, one enzyme hypothesis Not all proteins are metabolic (ex: keratin), so hypothesis is now one gene, one polypeptide

Central Dogma of Molecular Genetics: Crick Information coded in DNA is transcribed into mRNA and then translated into proteins DNA  RNA  protein Collectively known as gene expression

DNA vs. RNA Double stranded Single stranded Ribose sugar Bases: A, U, C, G U pairs with A Found in nucleus or cytoplasm Double stranded Deoxyribose sugar Bases: A, T, C, G Remains in nucleus

3* Types of RNA mRNA: carries DNA message from nucleus to cytoplasm tRNA: carries amino acids from cytoplasm to ribosome rRNA: forms part of ribosomes *other types of RNA exist but we will talk about those later

Steps in Gene Expression Transcription RNA processing (eukaryotes only) Translation Prokaryote Steps occur simultaneously Eukaryote Steps are separate

The Genetic Code Made of 3 letter codes: codons (found on mRNA) It is the same in almost all organisms Redundant: more than one codon for some AA’s NOT ambiguous: each codon codes for 1 amino acid

Overview of Protein Synthesis Begins with DNA Transcription: in nucleus, DNA message copied into mRNA mRNA is edited prior to leaving the nucleus (eukaryotes) Translation: mRNA message translated into amino acids at ribosomes

17.2 Transcription is the DNA-directed synthesis of RNA

Transcription Components necessary: RNA polymerase enzyme Promoter Separate DNA strand, add RNA nucleotides 5’3’ Promoter DNA sequence where transcription begins Different in prokaryotes and eukaryotes Terminator DNA sequence where transcription ends Prokaryotes only Transcription unit DNA to be transcribed into mRNA

Transcription: Initiation RNA polymerase recognizes and binds to promoter “upstream” of gene to be transcribed RNA polymerase unwinds DNA

Transcription: Elongation RNA polymerase moves along template strand of DNA adding complimentary RNA nucleotides Reads in 3’5’ direction This means mRNA is synthesized 5’3’ direction A – U; G – C

Transcription: Termination Terminator sequence in DNA is transcribed Signals to polymerase to detach from DNA and release transcript

17.3 Eukaryotic cells modify RNA after transcription

RNA processing Eukaryotic mRNA must be modified: Exons: coding sequences of DNA (“ex”pressed) Introns: non-coding regions, must be cut out by enzymes 5’ cap and poly-A tail added to protect mature mRNA